Primary effusion lymphoma (PEL) is a rare type of lymphoma that arises in the body cavity without detectable masses. It is associated with human herpes virus-8 (HHV-8), Epstein-Barr virus (EBV), and human immunodeficiency virus (HIV). Recently, PEL unrelated to viral infection has been reported and it has been termed HHV-8 unrelated primary effusion lymphoma-like lymphoma (HHV-8 unrelated PEL-like lymphoma). Here, we report a case of HHV-8 unrelated PEL-like lymphoma in an 80-year-old woman. Chest X-ray and computed tomography revealed left-sided pleural effusion. Pleural effusion analysis and mediastinoscopic biopsy showed atypical cells that had originated from the B cells. The cells were positive for CD20 and bcl-2, but negative for CD3, CD5, CD21, CD30, CD138, epithelial membrane antigen, and HHV-8. Serological tests for HIV and EBV were negative. Considering the patient``s age, further treatments were not performed. She has shown good prognosis without chemotherapy for more than 18 months.